A demonstration sparked by the Mexican government’s announcement that 43 student teachers disappeared by police in the southern city of Iguala six weeks ago were probably massacred in a rubbish dump, ended at the weekend with masked protesters setting fire to the wooden door of the ceremonial presidential palace in Mexico City’s main Zócalo plaza.

The protesters broke away from the otherwise peaceful demonstration as it drew to a close, tearing down the protective metal fences set up around the palace at its imposing door before they set it on fire. Clashes with riot police followed before the square was cleared.

Anger over the disappearance of the students, after they were attacked by municipal police in Iguala on 26 September, has been mounting in recent weeks. Protests have included large marches, and attacks on public buildings and bus stations.

Over time the focus of the protests has moved from the demand for the students to be found to criticism of the government’s handling of the investigation, which it took over from state authorities 10 days after the events.

Many protesters in Mexico City carried handmade banners with the words Ya me cansé (“I’ve Had Enough” or “I’m Tired”), in reference to a comment made by Mexico’s attorney general, Jesús Murillo, at the end of the press conference on Friday.

The phrase has been turned on its head to express public exhaustion with both the violence that has taken hold in many parts of Mexico, where organised criminal activity is protected by corrupt authorities, as well as the federal government’s failure to act against it, which many believe underpins the events in Iguala.

The US-based group Human Rights Watch has described the events in Iguala as the worst case of abuse to take place in Latin America in the past few decades. The organisation’s Americas director, José Miguel Vivanco, said: “These killings and forced disappearances reflect a much broader pattern of abuse and are largely the consequence of the longstanding failure of Mexican authorities to address the problem.”

Protesters also chanted: “It was the state”, in an effort to push home the message that the federal authorities have yet to accept the depth of the institutional crisis exposed by the apparent massacre.

The march in the capital came in direct response to the government’s announcement on Friday that its investigation has established that dozens of young people were massacred in a rubbish dump outside the town of Cocula, that borders Iguala.

Murillo said it took place a few hours after municipal police arrested dozens of students in the city and handed them over to a drug gang, Guerreros Unidos. The mayor of Iguala had allegedly been in league with the gang since he took office two years ago.

The students, from a radical teacher training college about two hours’ drive away, were in Iguala to commandeer buses to use in a later protest.

Murillo said the investigation has corroborated information given by arrested gang members who confessed to participating in the massacre, that the victims were incinerated in a huge funeral pyre that burned for 14 hours. He said the ashes and charred remains left after the fire burned itself out were collected in plastic bags and disposed of in a nearby river; some remains have now been retrieved.

He said a laboratory in Austria has been contracted to try to identify the remains, as the Mexican authorities do not have the technological capacity to do so.

Parents of the students have claimed the government wants to close the case. They have said they will continue to hope their children are alive until there is scientific evidence to the contrary.

Before he cut the press conference short, Murillo dismissed a question about why neither soldiers nor federal police stationed in Iguala had intervened when the municipal police were attacking and arresting the students. “If the army had come out at that moment, who would they have supported?” Murillo asked. “Obviously the answer would have been the legal authorities and it would have been a much bigger problem.”

Such answers do not satisfy the protesters and international human rights groups who now regularly describe what happened to the students as a crime of state.